1. Field of the Invention
The present invention relates to an inlet guide vane which is installed at a suction port into which a fluid is sucked by the rotation of an impeller and adjusts the suction volume and flow direction of the fluid, a turbo compressor, and a refrigerator.
Priority is claimed on Japanese Patent Application No. 2008-027070, filed Feb. 6, 2008, the content of which is incorporated herein by reference.
2. Description of the Related Art
As refrigerators which cool or freeze objects to be cooled, such as water, a turbo refrigerator or the like including a turbo compressor which compresses and discharges a refrigerant (fluid) by an impeller is known. In a compressor, when a compression ratio increases, the discharge temperature of the compressor becomes high and the volumetric efficiency thereof degrades. Therefore, the compressor is adapted to perform compression of refrigerant in a plurality of stages. For example, a turbo compressor which includes two compression stages provided with an impeller and a diffuser and compresses a refrigerant sequentially in these compression stages is disclosed in Patent Document 1 (Japanese Patent Unexamined Publication No. 2007-177695).
Such a turbo compressor is provided with a suction port for allowing the refrigerant to be sucked thereinto by the rotation of the impeller of the first compression stage, and a plurality of inlet guide vanes for adjusting the suction volume and flow direction of the refrigerant are arranged in parallel in a peripheral direction in this suction port.
Each inlet guide vane includes, for example, a rod-like shaft and a plate-like vane body connected to the shaft where directions of their axes are arranged on the same line, and is molded as a cast product. In this inlet guide vane, the shaft is connected to and supported by a drive mechanism, and the vane body is installed so as to protrude radially inward from an inner peripheral surface of the suction port toward a central portion thereof. Also, the suction volume and flow direction of the refrigerant sucked in are adjusted according to the angle of attack (rotating angle) of each inlet guide vane by rotating each inlet guide vane around the axis by the drive mechanism.
Additionally, as this type of inlet guide vane, there is one in which the vane body is formed in the shape of a flat plate or one in which a side surface (side surface which faces an impeller) on the side which becomes positive pressure and a side surface on the side which becomes negative pressure are formed in the shape of an aerofoil as curved surfaces (for example, refer to Patent Document 2 (Japanese Patent Unexamined Publication No. 2007-120494)).
However, in the inlet guide vane in which the vane body is formed in the shape of a flat plate, while the manufacture (molding) of the inlet guide vane is easy, the thickness of the vane body is constant from the inner peripheral surface of the suction port toward the central portion with a large flow velocity. Therefore, the flow of the refrigerant is disturbed, and the pressure loss becomes large. For this reason, there is a problem in that performance deterioration of the turbo compressor is caused.
Meanwhile, in the inlet guide vane in which the vane body is formed in the shape of an aerofoil, the side surface on the side of positive pressure and the side surface on the side of negative pressure are formed by curved surfaces. Therefore, the suction volume and the flow direction of a refrigerant can be adjusted without disturbing the flow of the refrigerant, and the pressure loss can be made small.
However, since this type of inlet guide vane is molded as a cast product, it is difficult to form the side surface on the side of positive pressure and the side surface on the side of negative pressure as curved surfaces with precision by casting. Additionally, it is necessary to machine the shaft after casting, and at this time, reference setting is performed with the vane body held. However, if both the side surfaces of the vane body are formed by curved surfaces, the reference setting becomes difficult. For this reason, there is a problem in that it is difficult to manufacture the inlet guide vane with high precision.